Fibres of various types are used today to an increasing degree for i.a. reinforcement of cast materials. Thus, reinforced concrete can be produced by adding steel fibres directly during the actual mixing process, which must then be distributed very carefully and uniformly if the finished concrete is to have the required homogenous and isotropic properties. However, this has not been possible to a satisfactory degree by means of the conventional dosing methods which tend to feed the steel fibres in the form of more or less tangled lumps.
The Danish published publication 153 450 B discloses a method and an apparatus for improving steel fibres which are present in bundles or packed lumps, and which, directionally oriented, are to be dosed to an airborne stream of material, such as a sprayed concrete mass. This takes place by tearing the bundles or the lumps apart in preferably a rotating drum with inwardly facing pegs, and gradually discharging the loosened steel fibres during the rotation through variable opening in the drum on an inclined chute, where the fibres are replaced by sliding down the chute under the action of gravity, said chute being constricted in a direction toward the lower end. The fibres now unidirectional are then sucked by a strongly sucking air stream into a pipe stub and further into a transport conduit, in which the unidirectional fibres are fed in an even flow to the mouthpiece in a spray assembly and are sprayed together with the concrete mass mentioned by way of example onto a surface. Tangled fibres can hereby effectively be loosened from each other and be conveyed in an evenly dosed stream with unidirectionally oriented fibres to and be used in e.g. a spray assembly for successive application of fibre-filled concrete on a surface. However, this known method is unsuitable when the fibres are to be used as reinforcement in cast concrete. The reason is that in this case the fibres are to be fed to the concrete mixer evenly and uniformly within a relatively short period of time in a predetermined portion in a loosened, but precisely not unidirectional state.